connecting problem

[Nifoxeli]

A school mate and i made a mangos 2.0.12 server it works fine we both can connect and other classmates can connect to. But when some people try to connect they got "unable to connect" and everyone copied my wow client folder with correct ips and stuff. Everyones firewall is letting wow through (some even dont have there firewall on) and they cant connect, so that cant be the problem. If had an private server before but if never encountered this problem. And i have searched this forum for about 4 hours. I could have missed something but i dont think so.

Does anyone know what to do? I'm very confused and we'd like to play wow with the whole class. I'd really appreciate some help with this.